Propagation of a Surface Magnetoelastic Wave in a Ferromagnet Near the Orientation Phase Transition
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Propagation of a Surface Magnetoelastic Wave in a Ferromagnet Near the Orientation Phase Transition I. V. Mal’tseva, *, I. V. Bychkova, b, D. A. Kuz’mina, b, and V. G. Shavrovc a Chelyabinsk
State University, Chelyabinsk, Russia Ural State University (National Research University), Chelyabinsk, Russia c Kotel’nikov Institute of Radioengineering and Electronics, Moscow, Russia *e-mail: [email protected]
b South
Received December 30, 2019; revised December 30, 2019; accepted January 10, 2020
Abstract—The frequency dependences of the group velocity and the damping of a magnetoelastic surface wave have been studied at various values of an external magnetic field and various angles of propagation. The group velocity bursts are observed at frequencies, at which peaks of surface wave damping take place. The behavior of a surface magnetoelastic wave is also studied near the orientation phase transition. In the phase transition point, the group velocity is changed by 1%. The dependences of the damping along the surface at various angles of propagation indicate the nonreciprocal wave nature. In this work, all the dependences have been obtained using computer calculations and the ferromagnet parameters are taken to be typical for iron– yttrium garnet. Keywords: ferromagnet, magneto elasticity, phase transition, surface wave DOI: 10.1134/S1063783420060141
1. INTRODUCTION It is well known that acoustic waves in a ferromagnet crystal can interact with a magnetic subsystem, generating a magnetoelastic wave that is a combination of a stress wave and a spin wave. The first studies on the interaction of magnetic and elastic subsystems of magnets were performed by Turov and Irkhin [1]; Akhiezer, Bar’yakhtar, and Peletminskii [2, 4]; and Kittel [3]. They predicted the existence of coupled magnetoelastic waves in ferro- and antiferromagnets. Those works were foundational at the birth of a new field of physics of magnetoordered materials, i.e., magnetoacoustics. At present, magnetoacoustics is widely used in electronics and microwave engineering [5–7]. A surface magnetoelastic wave appears as a result of the interaction of elastic waves at the crystal surface with the body and surface spin waves. The propagation of surface magnetoelastic waves has been extensively studied in many theoretical and experimental works (review [8] and Refs. in it). The magnetoelastic interaction is known to be relatively weak, but in the vicinity of the orientation phase transition, it can be quite strong and substantially influence the dynamic and static properties of magnets. This is related to the compensation of the crystal anisotropy field by an external magnetic field. In this work, we study the dependences of the group velocity and relative damping of a surface magnetoelastic wave of a cubic ferromagnet on the fre-
quency and an external magnetic field far from and near the orientation phase transition. 2. SETTING UP THE PROBLEM Figure 1 shows the problem geometry. A crystal occupies half-space y > 0. External dc magnetic field H0 and magnet
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